220 CHAP. XXIV. CARBOHYDRATE-FORMATION 



the normal. It was exposed to light of the sky from 9 a.m. 

 to 3 p.m. The oxygen evolved was found to be 0-70 c.c. 

 at 20 C. and pressure of 762 mm. The weight of the 

 oxygen was 0-92 mg. and that of the carbohydrate pro- 

 duced was o-8o mg., giving a carbohydrate-factor of 0-87. 

 Determinations made with six other specimens gave very 

 similar results. This would appear to indicate that, in 

 specimens previously kept in feeble light, with a starch- 

 content below the normal, the production of glucose is 

 relatively the less. 



The results obtained with plants grown in light of 

 different degrees of intensity may be simply stated as follows. 

 The constant value 0-8906 of the oxygen-carbohydrate 

 factor in normal specimens undergoes a definite variation 

 according to the previous conditions, plants from a sun- 

 exposed pond exhibiting the higher value, those from 

 semi-darkness the lower. 



Summary 



The method of determination of the amount of the 

 photosynthetic product from the amount of oxygen evolved 

 is free from many sources of error. It is simple and direct 

 and requires no complicated chemical analysis. 



The oxygen-carbohydrate factor for normal specimens of 

 Hydrilla is 0-8906. The increase of weight in the plant 

 may be calculated by multiplying the weight of oxygen 

 evolved by the constant carbohydrate-factor. 



The actual increase of weight due to photosynthetic 

 production of carbohydrate is directly obtained by means 

 of a sensitive balance. In simultaneous determination, the 

 volume of oxygen evolved is collected in the Eudiometer, 

 while the increase of weight is determined by the balance. 

 The results obtained by the indirect and the direct methods 

 are found to be in the closest agreement with each other. 



The method of the investigation of photosynthesis has 

 been rendered so sensitive that records may be obtained of 



